Hydrofracking for shale gas, oil shale, and geothermal energy

MINE 292 – Lecture 23

John A. Meech

What is Hydraulic Fracturing?

• HF is a method to transmit fluid or gas pressure to create cracks or open existing cracks in hydrocarbon-bearing rock to allow gas or oil to flow more freely from the formation to the wellbore

• Process is known as Stimulation

What is Hydraulic Fracturing?

• Method of HF depends on:– Type of well (vertical or horizontal)– Type of well construction (cement/casing)– Type of fracturing fluid– Cost of method– Wells are fractured from 8 to 40 times over their lives

• Methods– Pulsed Pressured Water (weeks)– High-pressure liquid propane gel (two days)– Explosives (not for shale gas)

Major Concerns

• Waste water treatment and disposal

• Safety of chemicals used

• Possibility of aquifer contamination

Fracturing rocks at depth

• Suppressed by confining pressure from overlying rock

• Tensile fractures require crack surfaces to move apart

• Confining pressure prevents movement

• Effective stress is reduced by increasing fluid pressure within cracks

• Minimum principal stress is in tension and exceeds tensile strength of the material

• Fractures are oriented perpendicular to minimum principal stress

• Hydraulic fracturing in wellbores sometimes used to determine orientation of principle stresses

Fracturing rocks at depth

Hydraulic fracturing is also applied:

– To stimulate groundwater wells– To precondition or induce rock to cave in mining– To enhance waste remediation (hydrocarbon waste or spills)– To dispose of waste by injection into deep rock formations– To measure rock stress– To enhance permeability for enhanced geothermal systems– To increase injection rates for CO2 sequestration

Fracturing rocks at depth

• Fluid pressure exceeds pressure gradient of the rock

• Proppant used to prevent or slow closure of cracks• silica sand or resin-coated sand• ceramic beads and other particulates

• Fluid leaking into permeable rock must be controlled or else it can exceed 70% of injected fluid

• Fracking is often performed in cased wellbores

• Zones to be fractured are accessed by perforating casing

• Pressures can reach as high as 100 Mpa

• Injection rates can reach up to 265 L/s

Fracturing rocks at depth

• High-viscosity fracturing >>> large dominant fractures

• 'Slickwater' (high rate) fracturing >>> small dispersed micro-fractures

• Fracture fluid contains water-soluble gels (guar gum) to increase viscosity and deliver proppant into formation

• Fluid injected into the rock is a slurry of water (90%), proppants (9.5%) and chemical additives (0.5%)

• Foams, and compressed gases (N2, CO2 and air) sometimes used

Typical Chemical Additives

Acids - HCl (5-28%) or acetic acid for cleaning perforations Salt - NaCl to delay breakdown of gel polymersPolyacrylamide - to minimize fluid/pipe frictionEthylene glycol - to prevent scale formationBorates - to maintain fluid viscosity as temperature risesNa2CO3 / K2CO3 - to maintain effectiveness of cross-linkers

Glutaraldehyde - to disinfect the waterGuar gum (water-soluble gels) - to increases viscosityCitric acid - to prevent corrosion

Monitoring

• Measure pressure and rate of growth of fracture

• Measure properties of fluid and proppant

• Model length, width, & connectivity of propped fracture

• Inject radioactive tracers to determine profile and locate fractures

• Monitor micro-seismicity using geophones to estimate size and orientation of fractures

• Install tiltmeter arrays to monitor strain

Environment

• Practices must become transparent (IP issues)• Air• Water• Injected Fluid (chemicals)• Flowback• Seismicity• Health Effects

Environment

• Practices must become transparent (IP issues)• Air• Water• Injected Fluid (chemicals)• Flowback• Seismicity• Health Effects

- methane releases- toxic gases- CO2

Environment

• Practices must become transparent (IP issues)• Air• Water• Injected Fluid (chemicals)• Flowback• Seismicity• Health Effects

- Huge volumes- 1.2 to 3.5 M gal/stimulation- Europe is higher due to depth

Environment

• Practices must become transparent (IP issues)• Air• Water• Injected Fluid (chemicals)• Flowback• Seismicity• Health Effects

- 35 out of 1,000,000 wells have caused contamination of ground water- Some chemicals are known carcinogens- Some chemicals are proprietary

Environment

• Practices must become transparent (IP issues)• Air• Water• Injected Fluid (chemicals)• Flowback• Seismicity• Health Effects

- Dissolved metals, brine, radioactivity - water treatment required at site

Environment

• Practices must become transparent (IP issues)• Air• Water• Injected Fluid (chemicals)• Flowback• Seismicity• Health Effects

Microseismic events (1.5-3.0)Very few wells have caused earthquakes of concern

BC Oil and Gas Commission concluded 38 earthquakes from 2.2 to 3.8 occurred in Horn River Basin from 2009 to 2011 near pre-existing faults

Environment

• Practices must become transparent (IP issues)• Air• Water• Injected Fluid (chemicals)• Flowback• Seismicity• Health Effects Short- and long-term exposure to

contaminated air & water and radon

Media Coverage

• Gasland - Josh Fox

• Truthland - Colorado Oil and Gas Conservation Commission (COGCC)

• Promised Land - Matt Damon

• Fracknation - Phelim Mcaleer

"New" Technologies

• Hydrofracking has been in use since late 1940s• Directional-drilling has evolved to an accuracy

previously unattainable• "Game-Changer" technology with respect to

fossil fuels as an energy source• These are clean techniques – no question• Resistance exists due to "hidden-agendas"

Land Disturbance – much reduced

6 wells (8 fracs/well) 48 vertical wells

Vertical vs. Horizontal

• Alberta– 70% in 2012

• B.C.– 89% in 2012

• Saskatchewan– 60% (2009-12)

Natural Gas Sources

Shale Gas

Shale gas has been produced for over 100 years in the Appalachian and Illinois Basins in the US

Hydraulic Fracturing was first used in late 1940s

New Drilling technologies has accelerated development and evolution of shale gas

World Shale Gas Reserves

Shale Gas Reserves – top 15 1. China 36 Tm3

2. United States 24 Tm3

3. Argentina 22 Tm3

4. Mexico 19 Tm3

5. Indonesia 18 Tm3

6. South Africa 14 Tm3

7. Australia 11 Tm3

8. Canada 11 Tm3

9. Libya 8 Tm3

10. United Kingdom 7 Tm3

11. Algeria 7 Tm3

12. Brazil 6 Tm3

13. Poland 5 Tm3

14. Pakistan 2 Tm3

15. Ukraine 2 Tm3

PriceWaterhouseCoopers

"By 2035, shale oil production could boost world economy by up to $2.7 trillion. US exports could reach 12% of world’s total oil production — 14M bbl/day revolutionizing global energy markets for many decades"

Shale gas exploration has revealed deep under-ground shale deposits of "tight oil" or shale oil

Canadian Shale Gas

Equipment Required During Operation

Equipment Required During Operation

Casing

Hydraulic Fracturing

First Commercial HF – Oklahoma, 1949

Hydraulic Fracturing

Location Relative to Ground Water

Location Relative to Ground Water

Permeability Ranges

• mD = milliDarcy (1 Darcy = 10-12 m2)

Permeability and Darcy's Law

xP

where

ν = superficial fluid velocity (m/s) κ = permeability (m2) µ = dynamic viscosity (Pa·s) ΔP = applied pressure (Pa) Δx = thickness of the bed (m)

Four Step Process

Step 1• Pressure the reservoir rock using a fluid to create a fracture

Step 2• Grow the fracture by continuing to pump fluids into the fracture(s)

Step 3 • Pump proppant materials into the fracture (contained in fracture fluid)

Step 4 • Flow-back to the well to recover fracture fluids while keeping proppant in

place

Perforating Gun

Frac-pumping Unit

Data Collection Van

Proppant Transfer Truck

Composition of Fracture Fluid

Micro-Seismic Monitoring

Data Collection of Micro-seismics

Location of Major Shale Gas Resources

Shale Gas Resources

U.S. Domestic Energy Consumption